990127-1.c

this is a gcc file, you can download it and learn its usetility, for further detail please look at t

main()
{
    int a,b,c;
    int *pa, *pb, *pc;
    int **ppa, **ppb, **ppc;
    int i,j,k,x,y,z;

    a = 10;
    b = 20;
    c = 30;
    pa = &a; pb = &b; pc = &c;
    ppa = &pa; ppb = &pb; ppc = &pc;
    x = 0; y = 0; z = 0;

    for(i=0;i<10;i++){
        if( pa == &a ) pa = &b;
        else pa = &a;
        while( (*pa)-- ){
            x++;
            if( (*pa) < 3 ) break;
            else pa = &b;
        }
        x++;
        pa = &b;
    }

    if ((*pa) != -5 || (*pb) != -5 || x != 43)
      abort ();

    exit (0);
}